The goal of this research is to discover the structural features of sensory neurons that define their capacities to code information. The emphasis is on the cytological design and pattern of connections of specific types of auditory neurons and their synaptic contracts at the levels of the cochlear nucleus, superior olive, and cochlea. This study relies on the Golgi and classical silver techniques to demonstrate neuronal architecture, silver-degeneration, histochemical, and autoradiographic methods to trace connections and to localize transmitter-related molecules, and electron microscopy applied to normal and experimental material. Sufficient details are obtained to correlate with electrophysiological recordings of sensory neurons, neurochemical studies of transmitter-related molecules, and electron microscopic observations of sensory synapses. The focus for these studies is on a definition of the circuits of specific morphological types of neurons linking inner and outer hair cells with those particular kinds of neurons in the cochlear nucleus which project to those types of neurons in the superior olivary complex forming the olivo-cochlear bundles. The resulting correlations provide a basis for exloring the mechanisms accounting for stimulus coding and information processing in the auditory system. The effects of noise and acoustic deprivation on the structure of central auditory synapses are also being studied.